(1) Field of the Invention
The present invention relates to a magneto-optical recording element used for a reloadable disk or the like. More particularly, the present invention relates to a high-performance recording element which is economically advantageous and has a low cost.
(2) Description of the Prior Art
Recently, research is vigorously made on highdensity recording using a vertical recording medium or magneto-optical recording medium. According to the recording method using a magneto-optical recording medium, in order to record large quantities of informations at a high density, converged laser beams are projected and the recording medium is locally heated to effect writing on bits, and reading is effected by utilizing the magnetic optical effect. An amorphous metal perpendicular magnetic anisotropy film consisting of rare earth-transition metal elements is mainly used as the recording medium.
The material of the magnetic anisotropy film should have such properties that the magnetic moment of the rare earth metal and the magnetic moment of the transition metal are stable in unparallel to each other, and requirements of amorphousness, perpendicular magnetic anisotropy, Kerr rotation angle and coercive force for the recording material should be satisfied. If only a Curie point recording material is taken into accout as the recording material from the practical viewpoint, Fe type ferrimagnetic materials are popularly used while the foregoing conditions are taken into consideration. As the rare earth element for the Fe type alloy, Gd, Tb, Dy and Ho are known, and in the transition metal system, addition of Co, Ni or the like to Fe as the indispensable component is known.
Among these rare earth element-transition metal type ferrimagnetic materials, since Tb-Fe, Tb-Co, Gd-Tb-Fe and Tb-Fe-Co systems have a high coercive force Hc, magneto-optical recording media comprising Tb as an indispensable element are most noted and many investigations are made on these magneto-optical recording media.
However, practical use of Tb involves various problems because Tb is most reactive to oxygen among heavy rare earth elements and is most expensive.
Since a perpendicular magnetic anisotropy film is easily obtained from TbFe or DyFe and a coercive force of TbFe or DyFe is large, microbits can be stably magnetized and TbFe or DyFe is fundamentally excellent as a recording medium. However, the Curie temperature is low. Namely, the Curie temperature of TbFe is about 120.degree. C. and that of DyFe is about 70.degree. C. Accordingly, recording can be easily accomplished by a laser of a semiconductor having a low output, but at the time of reproduction, since the Kerr rotation angle .theta. is small and the reproduction laser intensity should be reduced, the reproduction signal intensity is low and the performance index represented as .sqroot.R.theta.k (T) (in which R stands for the reflectance of the magnetic medium) is low and the carrier-to-noise ratio (C/N) is bad. The reason why .theta.k is small is that .theta.k is substantially proportional to the sublatice magnetization Ms(TM) and as approximately represented by the Brillouin function, .theta.k in the vicinity of room temperature is reduced to Tc is brought close to room temperature. Addition of Gd or Co may be considered as means for elevating Tc to about 200.degree. C. for increasing .theta.k. However, selection of such constituent elements have not been sufficiently studied.